Various electronic photographic methods have been known. The method is usually composed of the following procedures: An electrostatic image is formed on a photoreceptor by various methods, the electrostatic image is developed to a visible image by a toner or a developer each having a charge opposite to the polarity to the charge of the electrostatic latent image, the toner image is transferred onto a image receiving material such as a paper sheet according to necessity, and the toner image is fixed on the image receiving material by heating or pressing to obtain a copy.
The developing process of the electrophotographic method is principally classified into a single-component developing system and a double-component developing system. The developer to be used for the single-component developing system includes one comprised of a non-magnetic toner containing no magnetic material and a magnetic toner containing a magnetic material. Recently, the developing system using the non-magnetic single-component developer is mainly used.
In the developing system using the non-magnetic single-component developer, any carrier particle used in the double-component developer is not necessary and the developing member can be miniaturized and made light in the weight.
In the case of the double-component developing system, an apparatus for detecting the concentration of the toner in the developer and replenishing a necessary amount of the toner since it is necessary to hold the toner concentration in the developer which is a mixture of the toner and the carrier. Therefore, the developing apparatus is made large and heavy. The single-component developing system is preferred as a simple method since such the toner concentration controlling mechanism is not necessary in such the developing system. Recently, therefore, the developing apparatus using the single-component developer is widely used.
However, the double-component developing system is advantageous from the viewpoint of the design since the allowable range of the design of the materials and the using conditions is wide because the charge providing function is separated in such the developer. Consequently, the double-component developing system is widely used yet.
Recently, in the field of printer, ones using a LED or a LB as the light source are mainly used and the development of technology is directed to make higher the image resolution. The image resolution is recently improved to 600 to 1200 dpi from 300 to 400 dpi where dpi is dot number per 2.54 cm. Consequently, further precisely expression is required to the developing system.
In the case of the copying machine, the technology is also progressed to digitalization and a laser static latent image formation is mainly used. The developing system attainable the high resolution and precision of image is also required in such the method.
Responding such the situation, a toner having a small particle size is proposed in, for example, Japanese Patent Publication to Open for Public Inspection, hereinafter referred to JP O.P.I., Nos. 1-112253 and 2-284158. The size of toner particle is progressed to further smaller side.
Moreover, JP O.P.I. No. 61-279864 proposes a spherical toner having specified spherical coefficients SF-1 and SF-2. According to a study based on the example of the publication, the toner has a problem on the cleaning property thereof.
The toner image formed on the photoreceptor in the developing process is transferred onto the image receiving material in the transferring process. The toner remained on the photoreceptor after the transfer is removed in the cleaning process and stored in a discharged toner container. In the cleaning process, a cleaning means such as a blade cleaning, a far blush cleaning and roller cleaning is usually used.
Recently, a toner recycle system without formation of the discharged toner is generally utilized for the environmental preservation, in which the remained toner is reused in the developer.
When the small size toner is used in such the image forming system, the development with a sufficient stability cannot be attained for a long period because the toner is tend to be influenced by the stress in the developing apparatus such as the stress caused by the thin layer formation in the toner conveying of the non-magnetic single-component developer, the stress caused by a rubbing stress at the time of cleaning in the toner recycling system and in the toner conveying system and the contamination of the carrier in the double-component developer.